We have a Neptune Model: MDG5500AWW It is not heating up to dry clothes. Any ideas on what to check?

Hi mongo, First check the outlet for power, then pull out the dryer and unhook the vent and see if it fires up. If not you need to check ignitor, see if it glows. Ok?

You will have to take it apart and test the thermal fuse near the heating element. Most likely it is blown and will have to be replaced, but you will have to clean the drier out thoroughly. Every air duct will have to be removed and scraped and washed out to remove baked on lint deposits which is like concrete lining. This will burn so the manufacturer has installed the safeties to keep from having a house fire. Driers were the number one cause of fires at one time. Look at: http://www.youtube.com/watch?v=MMP7BW1lLs4 to see how. Also: http://www.youtube.com/watch?v=iBiRw-KElC4 ; http://www.youtube.com/watch?v=yFTZGgVisCI
When you finish cleaning the drier and install a new safety it is best to also replace the belt, too, because you do not want to have to disassemble it again and if the belt is over two years old you should replace it. The safeties are oval-shaped with a round center part containing the safety with two plug-on terminals for the wires.
Using an ohm meter you put a lead on each terminal with wires unplugged and if it's good you will have a reading of about zero; if it's bad it will read infinity.
Note that on most of the videos it does not show them washing out the parts, but this is important because it's the only way to really get the parts clean, just don't get motor wet or the capacitor if it has one. Vacuum out motor. I would move the drier out to your garage to have plenty of space to work. You also want to check your vent and clean it, also. The job is really easier than it sounds. There is no shortcut that will work; it has to be cleaned well. Before you re-assemble it make sure to use white lithium grease (high-temp grease) and grease all bearings. DrTom4444